Galaxies and X-ray PopulationsG. Fabbiano

Harvard-Smithsonian Center for Astrophysics

What are these X-ray sources?See Fabbiano 1989, 2006 ARAA

• LX >1037 erg s-1

– Accreting NS and BH in binary system (XRB)

– LMXB– HMXB

• LX >1039 erg s-1

– ULX

• LX <1037 erg s-1

– XRB + WD binaries– SNR

Two Topics

• The XRB XLF and ULXs– ‘special’ XRB or IMBH?

• LMXB populations in elliptical galaxies

Chandra HMXB XLF Star-Forming Galaxies

• Normalization – ~ SFR

• Slope– Flat power-law

• ULXs – high luminosity

HMXB XLF Grimm, Gilfanov & Sunyaev 2003

Chandra HMXB XLF Star-Forming Galaxies

• Normalization – ~ SFR

• Slope– Flat power-law

• ULXs – high luminosity

HMXB XLF Grimm, Gilfanov & Sunyaev 2003

ULX

ULXs and HMXB populations• Higher XLF normalization in

higher SFR galaxiesMineo et al 2012

• From complete nearby sample of 125 galaxies– 1 ULX per 0.5 M yr-1 SFRSwartz et al 2011

more ULXs with increased star formation

Mineo et al 2012

The Local XLF – SFR relation• NGC 2207/ IC 2163

Mineo et al 2014– 28 ULXs

• Number density and luminosity density of ULXs increases with SFR

The Local XLF – SFR relation• NGC 2207/ IC 2163

Mineo et al 2014– 28 ULXs

• Number density and luminosity density of ULXs increases with SFR

Chandra LMXB XLFold stellar populations

Kim & Fabbiano 2004; Gilfanov 2004

• Steeper at high luminosity than HMXB XLF– lack of high LX sources in older

stellar populations• To first order normalization

depends on integrated stellar mass

• LX(LMXB)~LK or M

Gilfanov 2004

Chandra LMXB XLFold stellar populations

Kim & Fabbiano 2004; Gilfanov 2004

• Steeper at high luminosity than HMXB XLF– lack of high LX sources in older

stellar populations• To first order normalization

depends on integrated stellar mass– LX(LMXB)~LK or M

Gilfanov 2004

ULXs in LMXB populations

• Galaxy stellar Mass – 1 ULX per 3.2×1010 M⊙Swartz et al 2011

• Rejuvenated stellar populations– Flatter XLFKim & Fabbiano 2010

107 ULXs in complete sample of 127 galaxies

D < 14.5 Mpc

ULXs in Elliptical galaxies

• Galaxy stellar Mass – 1 ULX per 3.2×1010 M⊙Swartz et al 2011

• Rejuvenated stellar populations– Flatter XLF

Young E Old E

Kim & Fabbiano 2010

XLF of ULX in all types of galaxies

• XLF consistent with XRB population

• Cut-off at 2-4×1040 erg s-1

Swartz et al 2011Complete nearby sample

XLF of ULX in all types of galaxies

• XLF consistent with XRB population

• Cut-off at 2-4×1040 erg s-1

• LX>2×1041 erg s-1 require new population– IMBH

Swartz et al 2011Complete nearby sample

LMXB populations and their origin

• Found in GCs and in the stellar field– GC formation ~100 times more

efficient Clark 1975

– Evolution of native field binary also possible see Verbunt & Lewin 2006 • LX ~ LK

• With the large Chandra LMXB samples and Hubble GC identification– Parameters governing GC-LMXB

formation– Are field-LMXBs from GCs?– LMXB properties and galaxy

evolution

Chandra: LMXB populations are linked to GCs1. Global properties / correlations

• The XLF normalization depends both on galaxy stellar mass and GC Specific frequency - Kim & Fabbiano 2004 – LX (Total, LMXBs) / LK ~1029 × SN

0.334 erg s-1 LK-1

Boroson, Kim & Fabbiano 2011

Joint Chandra - Hubble studies of LMXB and GC populations

• Which are the parameters governing GC-LMXB formation?• Are field-LMXB also formed in GCs?• What can we learn from the spatial distributions of GCs

and LMXBs?– LMXB properties and galaxy evolution

GC-LMXBs and GC parameterse.g., Angelini et al. 2001; Kundu et al. 2002, 2007; Sarazin et al. 2003; Jordan et al. 2004; Kim et al. 2006; Sivakoff et al. 2007; Paolillo 2011; Kim et

al 2013

• Not all GCs are equally good at making LMXBs

• Mass – LMXBs are preferentially found

in more massive GCs• Color / metallicity

– LMXBs are preferentially found in red (higher metallicity) GCs

• Compactness (rc or rh)– Encounter probability higher for

small rh: Γ~M1.5rh-2.5

Sivakoff et al 2007Virgo Survey, 11 galaxies

GC-LMXBs and GC parameterse.g., Angelini et al. 2001; Kundu et al. 2002, 2007; Sarazin et al. 2003; Jordan et al. 2004; Kim et al. 2006; Sivakoff et al. 2007; Paolillo 2011; Kim et

al 2013

• Not all GCs are equally good at making LMXBs

• Mass – LMXBs are preferentially found

in more massive GCs• Color / metallicity

– LMXBs are preferentially found in red (higher metallicity) GCs

• Compactness (rc or rh)– Encounter probability higher for

small rh: Γ~M1.5rh-2.5

Sivakoff et al 2007

GC-LMXBs and GC parameterse.g., Angelini et al. 2001; Kundu et al. 2002, 2007; Sarazin et al. 2003; Jordan et al. 2004; Kim et al. 2006; Sivakoff et al. 2007; Paolillo 2011; Kim et

al 2013

• Not all GCs are equally good at making LMXBs

• Mass – LMXBs are preferentially found

in more massive GCs• Color / metallicity

– LMXBs are preferentially found in red (higher metallicity) GCs

• Compactness (rc or rh)– Encounter probability higher for

small rh: Γ~M1.5rh-2.5

M81 GCs and GC-LMXBsCourtesy Andreas Zezas

Metallicity / Color is driving effect3 times more red than blue GC host LMXBs

+Kim et al 2013

GC - LMXBGC - LMXB

MASS Compactness/ Collision rate

Joint Chandra - Hubble studies of LMXB and GC populations

• Which are the parameters governing GC-LMXB formation?• Are field-LMXB also formed in GCs?• What can we learn from the spatial distributions of GCs

and LMXBs?– LMXB properties and galaxy evolution

….Shape of XLF suggests different GC and Field LMXB populations

• The GC-LMXB XLF flattens at LX < 5×1037 erg s-1

– lack of low-luminosity GC-LMXB Voss & Gilfanov 2007; Voss 2009; Kim et al 2009; D’Ago et al 2014

• It may also be flatter at high LX – More high LX LMXBs in GCs than in the field

Paolillo et al 2011; Luo et al 2012 – but better statistics are needed

Kim et al 2009

…but the field-LMXB population could contain some GC-born LMXBs

Irwin 2005, Kim et al 2009, Paolillo et al 2011; Mineo et al 2014

• Specific frequencies of GC-LMXBs and GCs are correlated

• There may be some correlation for field-LMXBs– Native + GC?

Mineo et al 2014

NGC 4649 – full coverage PI-Fabbiano

Chandra - Luo et al (2012), Hubble - Strader et al (2011)

425 LMXBs - 1516 GCs - 157 GC-LMXBs

• LMXB radial distributions follow those of parent GC population

NGC 4649 Radial Profiles - with full Chandra and Hubble coverage:

Mineo et al 2014

• Field-LMXB follow stellar light –possible discrepancies at large radii (see also Zhang et al 2012) – these are luminous LMXBs

• GC-LMXB distribution similar to stellar light except at center – lack of GCs

NGC 4649 Radial Profiles - with full Chandra and Hubble coverage:

Mineo et al 2014

What can we learn from 2D distributions?NGC4649 - D’Abrusco et al 2014a

Positions of 1516 GCs and 425 LMXBs

What can we learn from 2D distributions?Method - D’Abrusco et al 2013

1. K-th Nearest Neighbor density map DK=K/πRK

2 - Dressler et al 1980

2. Derive residual map relative to homogeneous distribution (radial dependence only)

3. Use Monte Carlo to establish Gaussianity and significance of residual features– Overall residuals– Contiguous spatial features

What can we learn from 2D distributions?NGC 4649

Highly significant 2D features detected in both red and blue GC distributions

Red GC Blue GC

2D features in the LMXB spatial distributionsNGC4649 - D’Abrusco et al 2014a

• Seen in GC-LMXBs following that of red GCs

• Also seen in luminous field-LMXBs

• GC ejection + differential dynamic friction?

GC LMXBRed GC

2D features in the LMXB spatial distributionsNGC4649 - D’Abrusco et al 2014a

• 2D feature in field-LMXBs

• GC ejection + differential dynamic friction?

FIELD LMXB GC LMXB

2D features in the LMXB spatial distributionsNGC4649 - D’Abrusco et al 2014a

• These are luminous field-LMXBs

• GC formation+GC ejection + differential dynamic friction?

FIELD LMXB GC LMXB

LMXB – LX > 1×1038 LMXB – LX < 1×1038

Conclusions• Chandra allows population studies of X-ray sources in galaxies• ULXs consistent with the high LX part of the XRB XLF

– Most ULXs due to massive highly accreting binaries– ULX with LX~1042 erg s-1 candidate IMBH

• LMXBs detected in both in GCs and in the stellar field• Dynamical GC formation enhanced in high metallicity (red) GCs, consistent with a

red giant role in the formation of these luminous LMXBs. GC mass and compactness are also factors

• Both GC formation and field binary evolution are important for producing LMXB populations– Correlations – Shape of XLF– Radial profiles

• 2D features in the GC and LMXB spatial distribution point to these sources as fossil remnants of the merging evolution of galaxies– More of this type of work is needed – We need Chandra and HST full coverage

Conclusions• Chandra allows population studies of X-ray sources in galaxies• ULXs consistent with the high LX part of the XRB XLF

– Most ULXs due to massive highly accreting binaries– ULX with LX~1042 erg s-1 candidate IMBH

• LMXBs detected in both in GCs and in the stellar field• Dynamical GC formation enhanced in high metallicity (red) GCs, consistent with a

red giant role in the formation of these luminous LMXBs. GC mass and compactness are also factors

• Both GC formation and field binary evolution are important for producing LMXB populations– Correlations – Shape of XLF– Radial profiles

• 2D features in the GC and LMXB spatial distribution point to these sources as fossil remnants of the merging evolution of galaxies– More of this type of work is needed – We need Chandra and HST full coverage

Conclusions• Chandra allows population studies of X-ray sources in galaxies• ULXs consistent with the high LX part of the XRB XLF

– Most ULXs due to massive highly accreting binaries– ULX with LX~1042 erg s-1 candidate IMBH

• LMXBs detected in both in GCs and in the stellar field– Dynamical GC formation enhanced in high metallicity (red) GCs, consistent with a

red giant role in the formation of these luminous LMXBs. GC mass and compactness are also factors

• Both GC formation and field binary evolution are important for producing LMXB populations– Correlations – Shape of XLF– Radial profiles

• 2D features in the GC and LMXB spatial distribution point to these sources as fossil remnants of the merging evolution of galaxies– More of this type of work is needed – We need Chandra and HST full coverage

Conclusions• Chandra allows population studies of X-ray sources in galaxies• ULXs consistent with the high LX part of the XRB XLF

– Most ULXs due to massive highly accreting binaries– ULX with LX~1042 erg s-1 candidate IMBH

• LMXBs detected in both in GCs and in the stellar field– Dynamical GC formation enhanced in high metallicity (red) GCs, consistent with a

red giant role in the formation of these luminous LMXBs. GC mass and compactness are also factors

• Both GC formation and field binary evolution are important for producing LMXB populations– Correlations – Shape of XLF– Radial profiles

• 2D features in the GC and LMXB spatial distribution point to these sources as fossil remnants of the merging evolution of galaxies– More of this type of work is needed – We need Chandra and HST full coverage

Conclusions• Chandra allows population studies of X-ray sources in galaxies• ULXs consistent with the high LX part of the XRB XLF

– Most ULXs due to massive highly accreting binaries– ULX with LX~1042 erg s-1 candidate IMBH

• LMXBs detected in both in GCs and in the stellar field– Dynamical GC formation enhanced in high metallicity (red) GCs, consistent with a

red giant role in the formation of these luminous LMXBs. GC mass and compactness are also factors

• Both GC formation and field binary evolution are important for producing LMXB populations– Correlations – Shape of XLF– Radial profiles

• 2D features in the GC and LMXB spatial distribution point to these sources as fossil remnants of the merging evolution of galaxies– More of this type of work is needed – We need full coverage with Chandra and HST

Why Chandra? Angular resolution is essential

• The Antennae galaxies – Chandra versus XMM-Newton

The End

XRB populations: pre-Chandrasee Fabbiano 1989, ARAA

• Outside the Local Group– Only most luminous XRBs

detected• a few ULX• ??? IMBH ???

NGC 6946 – Einstein Observatory

XRB populations: pre-Chandrasee Fabbiano 1989, ARAA

• Outside the Local Group– Integrated emission of galaxy (LX)• HMXB star-formation rate LX ~ LFIR

• LMXB stellar mass LX ~ LH

Einstein ObservatoryFabbiano, Feigelson & Zamorani 1982

Chandra – XRB population studies

• XRB populations characterized by – luminosity functions (XLF)– X-ray photometry – Source variability

NGC1316: Observed and corrected XLF Kim & Fabbiano 2003

Chandra – XRB population studies

• XRB populations characterized by – luminosity functions (XLF)– X-ray photometry – Source variability

Chandra color-color diagramPrestwich et al 2003

Chandra – XRB population studies

• XRB populations characterized by – luminosity functions (XLF)– X-ray photometry – Source variability

X-ray Transients in 3 E galaxiesBrassington et al 2012

Metallicity affects Red Giants properties –seeds for GC-LMXB formation

Ivanova et al 2012

• Average masses and number densities of red giants increase with metallicity

• LMXBs with high-metallicity giant donors drive higher MT rates and can appear as persistent systems

GC-LMXBs and GC parameterse.g., Angelini et al. 2001; Kundu et al. 2002, 2007; Sarazin et al. 2003; Jordan et al. 2004; Kim et al. 2006; Sivakoff et al. 2007; Paolillo 2011; Kim et

al 2013

Not all GCs are equally good at making LMXBs

Joint Chandra - Hubble studies of LMXB and GC populations

• Which are the parameters governing GC-LMXB formation?• Are field-LMXB also formed in GCs?• What can we learn from the spatial distributions of GCs

and LMXBs?– LMXB properties and galaxy evolution

Radial Profiles

• Do the spatial distributions of LMXB follow those of GCs or of the diffuse stellar light?– Insufficient GC identification of LMXBs and mixed GC

samples led to controversysee review Fabbiano 2006

– Complete Chandra and Hubble coverage of the main stellar body (including D25) have led to large samples and consistent results in NGC 1399 and NGC 4649 Paolillo et al 2011; Mineo et al 4649

NGC 4649 Radial Profiles - with full Chandra and Hubble coverage:

Mineo et al 2014

• Red GCs lacking in center and perhaps in excess at large radii, relative to stellar diffuse emission

• Blue GCs more radially extended than red

2D features in the LMXB spatial distributionsNGC 4278

D’Abrusco, Fabbiano & Brassington 2014